84 PETER OKKELBERG 



tion; but such an admission is not necessary for an explanation 

 of what actually takes place. 



Practically the same conclusion has been reached by Shull ('11) 

 in the case of plants. He says: 



May not maleness and femaleness be thought of as alternative states 

 which can be crudely analogized with the acidity and alkalinity of 



chemical solutions In some species the sexes appear to 



represent a much more strongly polarized (?) condition than in other 

 species, and a transition from the characters of the one sex to those of 

 the other is attained only with the greatest rarity, if at all; while in 

 other species the sex conditions may be so nearly balanced or neutral 

 that individuals are not absolutely determined in their sex relations by 

 their genotypic nature. . . . With such a conception of sex, it 

 also appears probable that sex may be influenced sometimes by external 

 factors as well as by internal ones, and in this case the preponderance 

 of one sex over the other, which has been observed in many animals 

 and .plants, need not be attributed alone to selective disorganization of 

 germ cells, a selective fertilization or a selective death rate, but might 

 conceivably be controlled to a certain extent by environmental condi- 

 tions, acting at some particular 'sensitive' period in the ontogeny of the 

 organism in question (pp. 363-364). 



^. Present status of the sex problem,. We may now ask whether 

 or not the view expressed above can be brought into harmony 

 with current opinions concerning sex determination. The gen- 

 erally accepted view is that sex is established at the time of fer- 

 tilization as a result of the presence or absence of so-called sex 

 chromosomes in the fertilized egg. This view was first expressed 

 by McClung in 1902. During the progress of his work on the 

 maturation of the germ cells in insects, he found a certain body 

 in the spermatocytes which was interpreted as being a sex-deter- 

 mining element. This body had been seen before by Henking 

 ('91), Montgomery ('98), and Pauhnier ('99), but it had not 

 been suspected that it might be a sex-determining factor. 

 McClung's statement concerning the function of the accessory 

 chromosome as it was called, was as follows : " . . . it is 



the bearer of those qualities which pertain to the male organism, 

 primary among which is the faculty of producing sex cells that 

 have the form of spermatozoa." This interpretation was quite 

 generally accepted. Previous to this time numerous theories 

 had been advanced concerning the cause of the appearance of 



